This invention relates generally to apparatus for controlling the opening and closing of the valves of an internal combustion engine, and pertains more particularly to apparatus for virtually eliminating the need for any adjustment to reduce the amount of lash decrease during the entire life span of a typical automobile engine.
The problem of lash change with respect to the valves of an internal combustion engine has long been recognized. As a result, various efforts have been made for adjusting valve lash. For instance, hydraulic lash adjusters have been employed to provide automatic adjustment. Also, the use of shims has become widespread, especially on engines utilizing four valves per cylinder. Obviously, the use of hydraulic lash adjusters involves additional cost and results in increased friction. On the other hand, the substitution of one thickness of shim for another, while rather inexpensive as far as materials are concerned, can be quite costly as far as labor is concerned.
Changes in lash are attributable to a number of factors. In some instances, the lash will increase and in others the lash will decrease. An increase in the length of the valve stem will, for instance, decrease the lash. Likewise, erosion of the valve seat can contribute to a decrease in lash, as well as erosion of the valve head. Where steel inserts are employed, such inserts tend to retract into the head when the head is made of aluminum. Where lash increases, in contradistinction to decreasing, there is also a problem. However, if cam and follower wear can be minimized, then a predetermined small amount of lash can be selected at the factory and the likelihood of increase in such lash will be substantially reduced. However, where the engine design is such that a definite increase in lash is apt to occur, it is recommended that the invention disclosed in my said copending application, Ser. No. 595,302, be employed.